For some reason after I enter my flight plan into my fmc and execute it. I review the plan and step through it. No discontinuity or anything. I activate my route, I turn on Vnav and Lnav, and no matter which runway I takeoff from, there's a magenta line that appears on runway heading. And my flight stays on the runway heading, no matter if I use SID or not. I can disable Lnav and get back to my route then once I re enable Lnav it takes me right back where I started, runway heading. I have my FD activated and everything, I can't figure it out. And it's on all three of my PMDG 737, 747, and 777. Any help would be appreciated, thanx a bunch.

Is the first waypoint a vector by any chance? If so, generally speaking, ATC would vector you towards the first fix, after that, you'd line select the fix you're trying to go to and replace VECTOR.

Kevin's probably right. Easy to get caught out by that. Need to manually fly to first actual fix either by hand flying or using HDG knob. Or use DIRECT TO or as Kevin says select the first actual fix then move it to top of the LEGS list. Be careful of terrain if the fix means making a major turn as the VECTORS may be there to steer you away from mountains! 

Edited December 30, 20187 yr by sloppysmusic

That was the issue! Thanks a million for the help, guys. I was panicking out. Lets try this flight again.

I should point out that if you're flying on VATSIM and a controller is online, the controller would vector you to your first fix, so you don't want to clear the vector until the controller tells you to proceed directly to the first fix.

On 12/30/2018 at 5:27 PM, Captain Kevin said:

I should point out that if you're flying on VATSIM and a controller is online, the controller would vector you to your first fix, so you don't want to clear the vector until the controller tells you to proceed directly to the first fix.

Just seen this tip, thanx again for the help. I actually just registered for VATSIM.